There is no currently identified exotoxin produced by Neisseria meningitidis, however, in 1931 a report was made of the production of a soluble substance with hemolytic and "protective" properties when meningococci were grown under conditions which produced heavy pellicle formation. We are attempting to reproduce the culture conditions described and assay the filtrates of these cultures for evidence of hemolysis of human red blood cells. Five strains have been grown in four different liquid media at 33 C under stationary conditions. Surface growing bacteria have been selected after 3-4 days of growth for inoculation of fresh media. After several passages, increasing pellicle formation has been noted. An assay measuring hemolysis using microtiter plates and absorbance at 415 (measuring hemoglobin) has been developed. Weak hemolysis, after overnight incubation, has been found in culture filtrates of some strains showing heavy pellicle formation. We are attempting to optimize assay conditions and investigate the properties associated with the filtrates producing hemolysis.